Is there a gustative equivalent to the olfactory “malodour”?

I have to say, I love the way you phrased the question. You are really just asking for a word that means bad taste, right?

"Malodor", according to my dictionary, is not a thing that smells bad; it means bad smell. So, are you asking for a word equivalent of bad taste, or a thing that tastes bad?

Ignore the second paragraph. I'm looking for a word for "bad taste".

While this doesn't exactly answer your question, if you were looking for an analog to "malodorous", I'd suggest simply "bad-tasting". If you accept that "bad-tasting" should be hyphenated, then it would qualify as a single word. Somehow, I can't quite get myself to suggest "bad-taste" for a noun, though.

I'd rather use "unpalatable" as an adjective. However, I'm looking for a gustative equivalent to "malodour", a noun.

Allow me to propose an English equivalent in the Noun category:
olfactory malodour = gustative malsaveur

Love the mental exercise you have triggered. I will be rummaging and ruminating these words for days. I am grateful. I LOVE playing with language(s). LD

If there is a single word for anything with a bad flavor, I would suggest avoiding it, as I also suggest avoiding the word "malodour." "Bad taste," and "bad smell" do the job, and anything else smacks of synonym searching.

What about off-flavour and off-taste? Will they be ok as a noun?

English, please. :)

How about poison? That's a noun that connotes a bad taste.

I'm looking for a word that denotes/means bad taste.

Rancidness? Though that applies to smell as well.

Etymologically, disgusting fits the bill, though we now use the word without any necessary connection to the physical sense of taste. Another word that works is yucky, which also isn't restricted to the sense of taste.